A conventional pneumatic caulking gun, such as the one disclosed in a Taiwan Patent Application with a Publication No. 563598, is as shown in FIG. 1, which includes a body 1 having a handle 11 to be hold by the users. The top of the handle 11 includes a placing base 12. Furthermore, a stopper 13 is mounted at the front end of the placing base 12 for placing thereon a silicon cartridge 4. A channel 14 is disposed between the handle 11 and the placing base 12 for being penetrated therethrough a control rod 5. An air inlet channel 111 and an air exhaust channel 112 are installed within the handle 11 for allowing the entry of the compressed air and the exhaust of the wasted air. Furthermore, both the air inlet channel 111 and the air exhaust channel 112 include inner threads 113 formed simultaneously. When being used, the silicon cartridge 4 is placed on the placing base 12, and the front portion of the silicon cartridge 4 is stopped by the stopper 13 while the end portion of the silicon cartridge 4 is disposed against a valve sheet 3 mounted within a valve seat 15. Then, the control rod 5 is driven backwardly by controlling the shift of the control rod 5. An air inlet 23 disposed on a rod seat 22 is then opened so that the compressed air enters an air chamber 21 of a valve cover 2 through the channel 14 and the air inlet channel 23, and then ejects from an air outlet 31 of the valve sheet 3 so as to push against a base block 41 in the end portion of the silicon cartridge 4. Accordingly, the silica gel is squeezed out from the silicon cartridge 4 and applied to working pieces. However, the users may feel tired since the air must be compressed by holding the handle 11 with hands. Furthermore, there might be dangerous situations caused by the user's uneven forces that render the user's losing his balance when the operation is on scaffolds. Moreover, when the silica gel is squeezed out from the silicon cartridge 4 by the compressed air, the exceed air pressure will keep on pushing the silicon cartridge 4 to cause a deformation of the silicon cartridge 4, and unnecessary silica gel will be squeezed out. Consequently, gel drops of the caulking are gun generated and thus the material is wasted.
Furthermore, an electric caulking gun is disclosed respectively in the patent specifications of U.S. Pat. No. 6,123,235 and TW00405447. In such a caulking gun, a conventional DC motor is used and a set of clutch is additionally mounted on the transmission system thereof. Accordingly, when the trigger is stopped pressing, the clutch is also activated to separate the DC motor from the pushing rod, and thus the resistance to the backward movement of the push rod is removed so that the counterforce generated by the viscid material is capable of pushing the push carriage back to retard the leakage phenomenon. However, the addition of the set of clutch mechanism can only “retard”, but not “stop” the leakage. Furthermore, the push rod of such a caulking gun is a rack. The engagement of a rack and a gear relates to a slide friction. The friction lost of the gear-rack engagement is far higher than that of a ball screw. Being a transpose mechanism, the gear-rack engagement is also weaker than the ball screw in structure strength. Therefore, when bearing the same load, a ball screw needs less material, and thus is smaller and lighter. Since the conventional device includes the above-mentioned defects, it is desired to provide an improved device for dispensing the viscid material without these defects.